N-(3,4-dichlorophenyl)propanamide is a herbicide which is known under a common name of propanil. Various processes for the preparation of propanil have been described. For example, GB903766, U.S. Pat. No. 3,382,280, GB1063528, CN1775745 and U.S. Pat. No. 3,158,650 disclose detailed preparation procedures for propanil.
GB903766 relates to preparation of propanil. Recrystallization of the final product has been carried out using aqueous methanol. GB903766 discloses the melting point of propanil as 91° C.
U.S. Pat. No. 3,382,280 discloses the preparation as well as recrystallization of propanil using cyclohexane.
However, none of the prior art mention about different crystalline forms having different physical forms and properties.
Characterization of propanil obtained by the processes described in the prior art is usually done by the analytical method such as NMR and melting point determination. In the Pesticidal Manual 13th Edition, propanil is described as colorless odourless crystals with a melting point of 91.5° C. The described melting points in the prior art is in the range of 91°-93° C.
Properties of different crystalline forms of a compound vary from one form to another in many ways. Examples of such properties specific to certain forms of a compound are colour, solubility, crystal size and shape, particle density, flowability, melting point, thermal stability and reactivity. For the large-scale manufacture and formulation of a commercial product such as propanil which is available as flakes, it is of crucial importance to know whether different crystalline modification of compounds exist or how can they be prepared and characterized. Such crystalline forms are of high relevance as they may lead to better bioefficacy and consequently a reduction in dosage of the pesticide which again has a direct impact on environment in a positive manner.
Propanil is a widely used contact herbicide. It is one of the more widely used herbicide in rice fields. It has been used at a dosage of up to 5.0 kg/hato control many broad-leaved and grass weeds, including Amaranthus retroflexus, Digitaria spp., Echinochloa spp., Panicum spp., and Setaria spp. It has been noted that large quantities of propanil is required for the effective control of the weeds which raise health and environmental concerns in using propanil.
Considering the wide scale use of propanil for effective post-emergent control of many broad-leaf weeds, a reduction in usage could be a better choice to have a direct impact on associated hazardous and toxicological problems on prolonged usage which in turn will help to continue the use of this herbicide effectively.
It has now been found out that propanil exists in a different crystal form having very advantageous properties such as better bioefficacy.
Disclosure on different crystalline modification of propanil as well as preparation procedure and characterization of any such crystalline modification of propanil is hitherto unknown.